Sewage Projects in Yokohama City

A. Case Study Overview

1. Activity/ Project Title:
Sewage Projects in Yokohama City
2. Themes:
Climate Change, Disaster, Infrastructure, SDGs
3. Summary:  

Through its sewage projects, the City of Yokohama is working to improve the water environment and reduce flood damage, thereby ensuring that the citizens of Yokohama can continue to lead their lives in safety and comfort. We are also working to take advantage of the sewage system’s resources to save energy and introduce renewable energy.

4. Sector:
City : Yokohama Environmental Planning Bureau
5. Implementation Period:

Since 1962

6. Project Site :
Within Yokohama City
7. Stakeholders&Partners:

B. Objective:

8. Objectives:
(1) Ensure a sanitary living environment.
(2) Improve the water environment
(3) Reduce flood damage
(4) Promote the reuse of resources

C. Activities

9. /Activities:
  • Sewage treatment
    In order to ensure safe and secure living conditions and a sanitary water environment, we treat sewage sludge by properly maintaining and operating sewage pipes, pumping stations, water reclamation centers, and sewage recycling centers. Nearly 100% of the city’s approximately 3.7 million citizens have access to sewer service.
  • Flood control measures
    To reduce flood damage, in addition to maintaining storm drains, storm water retention facilities are being developed in the pump drainage area.
  • Centralized treatment and reuse of sewage sludge
    Aside from collecting and efficiently treating the sludge discharged during the sewage treatment process, we are also striving to make effective use of renewable resources, such as sludge incineration ash and digester gas.

D. Challenges and solutions:

10. Challenges and solutions:

In light of the upcoming redevelopment period for the city’s sewage facilities, there is a need to step up the stock management of existing facilities.

In addition, in order to cope with increasingly intense downpours, we must also implement measures to deal with flooding. This will involve a perspective of adapting to the effects of climate change, such as promoting the use of green infrastructure.

E. Outcomes and Impacts:

11. Outcomes&Impacts:

As a result of intensive sewer development since the 1970s, Yokohama City’s sewer coverage rate has reached almost 100%. Today, it provides round-the-clock maintenance and management of sewer facilities, including 11 water reclamation centers, two sludge recycling centers, and approximately 11,900 kilometers of sewer pipes in order to provide sewer services to approximately 3.7 million residents.

In addition, as a result of the focused construction of facilities in areas that had a high risk of flooding, flood damage has been markedly reduced relatively to before the work.

F. Budget:

12. Budget:

252.4 billion JPY (FY 2020)

13. Source:
Sewer charges, general funds, state subsidies, corporate bonds, etc.
Through this e-learning content, you can see and learn the outline of the sewage works in Yokohama City.
Today’s topics are these items.
First, introduction of the city. Second, how Yokohama City developed sewerage system. Then, treatment technologies. And then, effective utilization of our assets. After that, comfortable water environment Yokohama has been achieving. At last, we’ll briefly introduce flood control measures done by Yokohama City.
First, let’s go on to the introduction of Yokohama City.
This bird’s-eyes view picture shows central urban area of Yokohama city.
You could get Mount Fuji behind of Yokohama Port in this slide.
It is the symbol in Japan. And Yokohama Port is very famous Japanese trade port.
Location of Yokohama city is the center of Japan, and nearby capital Tokyo.
And it takes about 30 minutes from Tokyo International Airport, HANEDA.
The city area is 435㎢, and the population is 3.8 million.
Yokohama is an international city in Japan. At the international stadium named Nissan Stadium, the final game of World Cup Rugby was held in 2019.
The final game of FIFA world cup soccer was held in 2002 as well.
Until now, many international sports events were held there continuously.
This is a picture of the international convention facilities at the bay area.
In 2017, ADB’s 50th annual meeting was held there, and 104 international conventions were held in 2018..
This slide shows population growth in Yokohama City and the improvement of water environment along its sewerage service expansion.
The blue line is city population growth, and red bars show the growth of sewerage service coverage.
Other lines show BOD concentrations of three major rivers in Yokohama.
You can see improvement of river water quality by sewerage service expansion.
Yokohama city’s sewerage service rate is almost 100%, over 3.7 million citizens have got services.
There are 11 wastewater treatment plants and 2 sludge treatment plants in Yokohama city.
Total sewer length is around 11,900km, it is almost the same as the distance from Yokohama to New York.
These facilities have covered the whole city area to give sewerage services.
Daily wastewater inflow in the whole city is approximately 1.6 million cubic meters per day.
Yokohama City operates wastewater collection systems comprised of “separate” and “combined” sewers.
According to the revision of national standards of sewer design, we started to develop separate sewers in the suburbs during 1970’s.
However, Yokohama City kept developing combined sewers in the old city area even after 1970’s because it costs a lot to change the wastewater collection system.
This slide shows sewer classification areas.
Combined sewer system has been applied to the old town area, which is yellow-colored in this map.
Separated sewer system has been applied to the suburbs.
Sanitary sewage is sent to wastewater treatment plants, properly treated, and discharged into rivers and the ocean.
Stormwater is discharged into rivers and the ocean in order to prevent inland flooding. .
Characteristics of sewerage development in the city of Yokohama is concentrated investment during 1980’s and early 90’s.
For 15years from 1981, over 1 billion USD of construction cost was invested each year and total investment was 19 billion USD.
As a result, we increased sewerage service rate over 90%. .
Total budget of Yokohama City is 36 billion USD in 2020.
7% of total city budget is Sewage Works budget. It’s approximately 2.5 billion USD.
Employees of Sewage Works is 823 people, it is equivalent to 1.9% of total employees in the city hall.
From here, we’ll explain treatment technologies that support our sewage works in Yokohama City.
First, wastewater treatment.
We selected conventional activated sludge method. It’s usually called CAS method.
Wastewater treatment with CAS method, first, starts with the grid chamber.
The second is primary sedimentation, the third is aeration, the forth is final sedimentation, and the last treatment is disinfection with chlorine.
CAS is very popular and standard treatment method in Japan especially in urban areas.
Meanwhile, recently we have been applying advanced treatment method called A2O that can remove nitrogen and phosphorus in addition to organic matters.
As this picture shows, the reaction tank is divided into anaerobic, anoxic, and oxic cells.
This slide shows why we’ve been applying A2O method.
Nitrogen and phosphorus cause red tide in closed water area.
Red tide is a huge outbreak of plankton such as water-bloom.
And it causes very bad smells and sometimes death of a huge number of fish.
These phenomenon deteriorate sightseeing industry as well as fisheries.
The upper table shows the average water quality of influent and effluent in all WWTPs in Yokohama City in 2018.
You can see that the water quality of effluent comply with the target value, which is the same as the regulations.
The lower table shows the removal rates of nitrogen and phosphorus.
We can understand that the removal rates by advanced method are higher than the ones by standard method.
This slide shows sludge treatment process flow.
Sewage sludge removed from wastewater in WWTP is transported to the sludge treatment plants and treated through these processes.
Thickening, digestion, dewatering, and incineration.
Then the volume of the sludge is drastically reduced.
This slide shows the reduction of the sludge volume through the treatment processes.
Through these processes, moisture and organic matters contained in the sludge can be removed or decomposed.
15,000 tons of the sludge generated everyday in Yokohama becomes 40 tons as incinerated sludge ash.
It means the weight can be reduced by a four hundredth.
Sludge has a serious odor problem.
In order to solve this problem, centralized sludge treatment system using pressurized pipeline has been selected in Yokohama city.
We started this system in 1988.
Thanks to this centralized treatment system, we could get odor-free transportation of odor sludge.
In addition, both of the two sludge treatment plants are located in the industrial areas near the seashore, where people are not allowed to live.
Yokohama city adopted this odor-free sludge treatment system for the first time in Japan.
We utilize treated wastewater and sewage sludge as resources and energy. On top of that, by utilizing upper part of underground sewage facilities as parks and laying optical fibers inside sewer pipes, we contribute to regional revitalization and realization of a highly information-oriented society
Because we have huge amount of wastewater inflow, most of them are discharged to rivers and the sea.
On the other hand, some of treated wastewater is used for the purposes shown in this slide after additional treatment such as sand filtration and ozonation treatment.
Reclaimed water is used for toilet flushing, small stream restoration, and heating and cooling resources.
This slide shows the example of recycling of wastewater in one of treatment plants in Yokohama.
Reclaimed water is transported through pressurized pipeline, represented by these blue lines.
Considering cost effectiveness, reclaimed water is sent to big commercial and municipal consumers near WWTPs as this picture shows.
When it comes to sludge, we don’t dump any sludge into landfill sites. We utilize all amount of incinerator ash as material such as backfill soil for construction works. As for digestion gas, we use them as power generation fuel or supplemental fuel for incineration. And recently we inaugurated sludge drying facility to produce coal alternative fuel in order to make more certain of our 100% reuse of sludge.
Small streams in the city area are usually reclaimed to build roads because the flow rate becomes lower along with urbanization.
But this picture shows an example of restoration of a small stream using treated wastewater.
The greenery along this stream is maintained in cooperation with the citizens and companies in the neighborhood.
This is also a good example for the promotion of sewage works.
This is another example of creation of comfortable space. We built a flood control reservoir under a park in collaboration between sewerage project and the public park project.
Flood control measures need to be taken to prevent flooding from sewers during heavy rains.
There are two classification of city areas in terms of the drainage system.
Stormwater can be removed from the natural drainage area to rivers or the sea using gravity flow.
However, stormwater in the pumping drainage area should be removed by pumping facilities.
Therefore, flood risks in the pumping drainage area is higher than in the natural drainage area.
That’s why Yokohama City applies stricter design standard for drainage pipes in the pumping drainage area.
Drainage pipes in the natural drainage area are designed with capacity that can convey at least 5-year return frequency stormwater.
In the pumping drainage area, pipes are designed with capacity that can convey at least 10-year return frequency stormwater.
This chart shows one of examples of countermeasures against flooding in pumping drainage area.
Nippa-Suehiro Trunk Sewer is a large-scale stormwater storage tank intalled along Tsurumi River.
When stormwater exceeds flow capacity of the drainage pipes in the catchment basin, excess stormwater is conveyed to Nippa-Suehiro Trunk Sewer.
It has a capacity with 410,000 cubic meters of stormwater storage and plays a major role in reducing flood damage in the area along Tsurumi River.
This is the end.